When milling out a tool or pipe in the well cuttings are generated that need to be removed from the milling site and collected. The bottom hole assembly that includes the mill also has what is sometimes referred to as a junk basket. These tools operate on different principles and have the common objective of separation of circulating fluid from the cuttings. This is generally done by directing the flow laden with cuttings into the tool having a catch chamber. The fluid is directed through a screen, leaving the cuttings behind. At some point the cuttings fall down into the collection volume below and outside the screen.
The operation of one type of such tool is illustrated in FIG. 1. In this known tool, flow comes from the surface through a string (not shown) and enters passage 10 in the tool 12. Flow goes through the eductor 14 and exits as shown by two headed arrow 16. Arrow 16 indicates that the exiting motive fluid can go uphole and downhole. The eductor 14 reduces pressure in chamber 18 all the way down to the lower inlet 20 on the tool 12. Arrow 22 represents fluid indicated by arrow 16 that has traveled down the annulus 24 between toll 12 and tubular 26 as well as well fluid below tool 12 that is sucked in due to the venture effect of the eductor 14. Entering fluid at lower inlet 20 goes through a tube 28 that has a hat with openings under it 30. Arrows 32 indicate the exiting flow out from under hat 30 that next goes to the outside of screen 34. At this point the cuttings are stopped by the screen 34 while the fluid goes on through and into chamber 18 as indicated by arrow 36. The stream indicated by arrow 36 blends and becomes part of the stream exiting eductor 14 as indicted by arrow 16. When flow into passage 10 is shut off, the accumulated debris on the outside of screen 34 simply falls down to around the outside of tube 28. The presence of the hat 30 keeps the debris from falling into tube 28 deflecting debris that lands on it off to the side and into the annular catch area in the tool 38.
This is how this tool is supposed to work when everything is going right. However, things don't always go right downhole and the operator at the surface using this tool in a milling operation had no information that things downhole may not be going according to plan. The main two things that can cause problems with this type of tool or any other junk basket tool is that the screen 34 can clog with debris. Those skilled in the art will appreciate that flow downhole in annulus 24 goes all the way down to the mill and enters openings in the mill to reach lower inlet 20 of the tool 12. If the screen clogs the downhole component of the flow indicated by arrow 16 stops. As a result, there is a diminished or a total lack of flow into the mill ports to remove the cuttings and take away the heat of milling. The mill can overheat or get stuck in cuttings or both. If the mill sticks and turning force is still applied from the surface, the connections to the mill can fail. Sometimes, without clogging screen 34, the mill can create cutting shapes that simply just ball up around the mill. Here again, if the balling up occurs, flow trying to go downhole in annulus 28 will be cut off. The inlet openings for the cuttings in the mill may become blocked limiting or cutting off flow into lower inlet 20.
What the operator needs and currently doesn't have is a way to know that a condition has developed downhole at the mill or at the screen 34 that needs to be immediately addressed to avoid downhole equipment failure. While some operator with enough experience cleaning up a hole may be able to do this by gut feel in certain situations like removing sand, using gut feel is not reliable and in milling as opposed to simple debris cleanout, rules of thumb about how fast the bottom hole assembly moves into sand when removing it from the wellbore are simply useless.
What is needed and provided by the present invention is a real time way to know if anything has gone wrong downhole in time to deal with the issue before the equipment is damaged. The tool of the present invention is able to sense flow changes through it and communicate that fact in real time to the surface. Those and other aspects of the present invention will become apparent to those skilled in the art from a review of the description of the preferred embodiment, the drawings and the claims which outline the full scope of the invention.